Nephew's request for help beyond me!

[Virgil]

Got this email from my nephew, but it's out of my league. Maybe someone here can help. His email:
Looking for a solution for injecting a set frequency signal (approx. 11 khz 5 volts/555 timer ckt) into 256 seperate video circuits.
Would be used while the video circuits were not being used. As of now, i have to do each video (camera) input seperately on an as needed basis. What I am considering is to have this signal injected on all circuits during off time.
What I use it for is to restore defective camera input signal. This little pulser restores a defective camera input, I guess by breaking down oxidation of connectors. Anyway, it restores video, so it can work. Basic circuit would have oscillator signal available continuously, and apply that signal on a time-shared basis to each of 256 camera input circuits. If you can give me an idea on what chips or circuits that could be used I surely would appreciate it very much. (End email)
Would appreciate your ideas on this,
Virgil

 

[Rich Andrews]

"Virgil" <oldfogie@earthlink.net> wrote in news:sNb9b.13535$Aq2.8580
@newsread1.news.atl.earthlink.net:

Got this email from my nephew, but it's out of my league. Maybe someone
here can help. His email:
Looking for a solution for injecting a set frequency signal (approx. 11
khz 5 volts/555 timer ckt) into 256 seperate video circuits.
Would be used while the video circuits were not being used. As of now, i
have to do each video (camera) input seperately on an as needed basis.

What I am considering is to have this signal injected on all circuits
during off time.

What I use it for is to restore defective camera input signal. This
little pulser restores a defective camera input, I guess by breaking down

oxidation of connectors. Anyway, it restores video, so it can work. Basic
circuit would have oscillator signal available continuously, and apply
that signal on a time-shared basis to each of 256 camera input circuits.
If you can give me an idea on what chips or circuits that could be used I
surely would appreciate it very much. (End email)

Would appreciate your ideas on this,
Virgil

The problem lies in that you are going to be driving 256 75 ohm loads all
at once. The cheaperst way to do that would be to set them up in a
parallel-series configuration so that an audio amp would drive it. Rather
impractical for a variety of reasons, but possible. If one had an
amplifier that had a regulated power supply, one could limit the P-P
maximum amplitude by turning it down a bit.

What he means by time-shared is unclear to me.

The right way to do it would be to use an array of DA's, but that gets a
bit expensive.

I am assuming that the 555 will drive the circuit to the levels he wants.
One could use a bunch of quad bilateral switches and that would reduce the
parts count by a factor of 3.n as the fanout of the 555 master clock would
have to be taken into consideration and you could use one QBS section to
drive the other switches. I am not sure if you could drive a 75 ohm load
with a QBS without the switch overheating.

According to my calcuations, the collective current that 256 circuits
would draw at 75 ohms each would be about 18 amps. One could use op-amps
I suppose since all you want is a square wave anyway. Raise the gain of
the opamp and the input impedance up and things might be OK.

What makes this project tough is the fact that he wants to drive 256 of
the critters. Without knowing what sort of infrastructure he has and his
budget, it also makes things a bit tought too.

r

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

 

[Virgil]

Thanks, Rich, I'll forward your reply to him. I don't know what he meant by timeshared either, maybe he meant to scan theough the inputs and do them one at a time?
Virgil
"Rich Andrews" <noway@yahoo.com> wrote in message news:Xns93F71D815667Amc2500183316chgoill@216.168.3.44...

"Virgil" <oldfogie@earthlink.net> wrote in news:sNb9b.13535$Aq2.8580
@newsread1.news.atl.earthlink.net:

Got this email from my nephew, but it's out of my league. Maybe someone
here can help. His email:
Looking for a solution for injecting a set frequency signal (approx. 11
khz 5 volts/555 timer ckt) into 256 seperate video circuits.
Would be used while the video circuits were not being used. As of now, i
have to do each video (camera) input seperately on an as needed basis.
What I am considering is to have this signal injected on all circuits
during off time.
What I use it for is to restore defective camera input signal. This
little pulser restores a defective camera input, I guess by breaking down
oxidation of connectors. Anyway, it restores video, so it can work. Basic
circuit would have oscillator signal available continuously, and apply
that signal on a time-shared basis to each of 256 camera input circuits.
If you can give me an idea on what chips or circuits that could be used I
surely would appreciate it very much. (End email)
Would appreciate your ideas on this,
Virgil



The problem lies in that you are going to be driving 256 75 ohm loads all
at once. The cheaperst way to do that would be to set them up in a
parallel-series configuration so that an audio amp would drive it. Rather
impractical for a variety of reasons, but possible. If one had an
amplifier that had a regulated power supply, one could limit the P-P
maximum amplitude by turning it down a bit.

What he means by time-shared is unclear to me.

The right way to do it would be to use an array of DA's, but that gets a
bit expensive.

I am assuming that the 555 will drive the circuit to the levels he wants.
One could use a bunch of quad bilateral switches and that would reduce the
parts count by a factor of 3.n as the fanout of the 555 master clock would
have to be taken into consideration and you could use one QBS section to
drive the other switches. I am not sure if you could drive a 75 ohm load
with a QBS without the switch overheating.

According to my calcuations, the collective current that 256 circuits
would draw at 75 ohms each would be about 18 amps. One could use op-amps
I suppose since all you want is a square wave anyway. Raise the gain of
the opamp and the input impedance up and things might be OK.

What makes this project tough is the fact that he wants to drive 256 of
the critters. Without knowing what sort of infrastructure he has and his
budget, it also makes things a bit tought too.

r

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

 

[Charles Schuler]

What he means by time-shared is unclear to me.

Perhaps he is seeking a demultiplexer that drives one output at a time?

 

[Virgil]

I forwarded Rich's email to him, haven't heard back yet.
"Charles Schuler" <charlesschuler@comcast.net> wrote in message news:Er-dnbudD_YRh_uiXTWJjQ@comcast.com...

What he means by time-shared is unclear to me.

Perhaps he is seeking a demultiplexer that drives one output at a time?

 

[Virgil]

Here is email I got from my nephew about this.

virgil:

just a bit more of info for circuit, would be that only one circuit at a time, would be pulsed by oscillator signal circuit. thats what i meant by timesharing. if this the 256th output were pulsed, i would say it would start over at number 1 output.

the biggest problem is the chip to switch with, and then probably counter/stepper circuit to control the switcher chip.

timing on each output could say 2 seconds. sure it could be changed later if needed. at any given time it would one signal in/ one signal out. and it is a video signal coming from closed circuit tv camera. 1 volt standard tv video signal.
thanks, cannot get outlook set up at work, but have downloaded stuff sci.electrlnics. repair at home. have more time at work.

gerald b.



I forwarded Rich's email to him, haven't heard back yet.
"Charles Schuler" <charlesschuler@comcast.net> wrote in message news:Er-dnbudD_YRh_uiXTWJjQ@comcast.com...

What he means by time-shared is unclear to me.

Perhaps he is seeking a demultiplexer that drives one output at a time?

 

[gerald blackard]

to all:
this is de nephew. gerald b. added info for quest. 256 video inputs
(1v)
need to pulsed one at a time from one signal source, namely square ware 50%
duty cycle around 11kc. signal would be on each input for about a second.
nothing critical on time. after pulsing each cam input, it would start over
again.
any ideas would be appreciated.
de nephew gerald b.



Virgil <oldfogie@earthlink.net> wrote in message
news:VEi9b.17515$Aq2.9131@newsread1.news.atl.earthlink.net...
Thanks, Rich, I'll forward your reply to him. I don't know what he meant by
timeshared either, maybe he meant to scan theough the inputs and do them one
at a time?
Virgil
"Rich Andrews" <noway@yahoo.com> wrote in message
news:Xns93F71D815667Amc2500183316chgoill@216.168.3.44...

"Virgil" <oldfogie@earthlink.net> wrote in news:sNb9b.13535$Aq2.8580
@newsread1.news.atl.earthlink.net:

Got this email from my nephew, but it's out of my league. Maybe someone
here can help. His email:
Looking for a solution for injecting a set frequency signal (approx. 11
khz 5 volts/555 timer ckt) into 256 seperate video circuits.
Would be used while the video circuits were not being used. As of now, i
have to do each video (camera) input seperately on an as needed basis.
What I am considering is to have this signal injected on all circuits
during off time.
What I use it for is to restore defective camera input signal. This
little pulser restores a defective camera input, I guess by breaking down
oxidation of connectors. Anyway, it restores video, so it can work. Basic
circuit would have oscillator signal available continuously, and apply
that signal on a time-shared basis to each of 256 camera input circuits.
If you can give me an idea on what chips or circuits that could be used I
surely would appreciate it very much. (End email)
Would appreciate your ideas on this,
Virgil



The problem lies in that you are going to be driving 256 75 ohm loads all
at once. The cheaperst way to do that would be to set them up in a
parallel-series configuration so that an audio amp would drive it. Rather
impractical for a variety of reasons, but possible. If one had an
amplifier that had a regulated power supply, one could limit the P-P
maximum amplitude by turning it down a bit.

What he means by time-shared is unclear to me.

The right way to do it would be to use an array of DA's, but that gets a
bit expensive.

I am assuming that the 555 will drive the circuit to the levels he wants.
One could use a bunch of quad bilateral switches and that would reduce the
parts count by a factor of 3.n as the fanout of the 555 master clock would
have to be taken into consideration and you could use one QBS section to
drive the other switches. I am not sure if you could drive a 75 ohm load
with a QBS without the switch overheating.

According to my calcuations, the collective current that 256 circuits
would draw at 75 ohms each would be about 18 amps. One could use op-amps
I suppose since all you want is a square wave anyway. Raise the gain of
the opamp and the input impedance up and things might be OK.

What makes this project tough is the fact that he wants to drive 256 of
the critters. Without knowing what sort of infrastructure he has and his
budget, it also makes things a bit tought too.

r

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

 

[Rich Andrews]

[posted and mailed]

"Virgil" <oldfogie@earthlink.net> wrote in news:r59ab.33260$NM1.15151
@newsread2.news.atl.earthlink.net:

Here is email I got from my nephew about this.

virgil:

just a bit more of info for circuit, would be that only one circuit at a
time, would be pulsed by oscillator signal circuit. thats what i meant

by timesharing. if this the 256th output were pulsed, i would say it
would start over at number 1 output.

the biggest problem is the chip to switch with, and then probably
counter/stepper circuit to control the switcher chip.

timing on each output could say 2 seconds. sure it could be changed
later if needed. at any given time it would one signal in/ one

signal out. and it is a video signal coming from closed circuit tv
camera. 1 volt standard tv video signal.

thanks, cannot get outlook set up at work,
but have downloaded stuff sci.electrlnics. repair at home. have more time

at work.

gerald b.

Virgil and Gerald,

Instead of thinking about running pulses through a switch, why not pulse
the enable/inhibit/strobe of the output chip(s)?

Anyway, if I have this right, he wants to send the output of an ocsillator
to the camera output? Isn't that a bit tough on the output circuit of the
camera? He may need a lot of drive to do that.

Try this circuit on for size.

http://www.nelnickrobotics.com/8to256dec.html

The drive to the circuit laid out could be a 4017 and the clock for the
counter could be his main oscillator divided by n to provide a 2 second
pulse. One could also use a RC circuit to provide timing.

Now if you need a true switch type function then you are going to have to
add something like a 4016 quad bilateral switch. To make matters worse,
you may have to add a transistor to switch enough current instead of the
switch. Thankfully transistors are dirt cheap.

I hope that helps!

r

I forwarded Rich's email to him, haven't heard back yet.
"Charles Schuler" <charlesschuler@comcast.net> wrote in message news:Er-
dnbudD_YRh_uiXTWJjQ@comcast.com...



What he means by time-shared is unclear to me.

Perhaps he is seeking a demultiplexer that drives one output at a
time?

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"